Frequency band shifter

ABSTRACT

A frequency band shifter for shifting a selected frequency band in a complex waveform, which frequency band is translated with its relative frequency, phase and amplitude relationships maintained to a reproduced lower frequency and, if desired, to a smaller frequency band for analysis, which translation is processed by manual or digital control with a master local oscillator control clock that provides protection against drift in frequency and phase throughout the system.

United States Patent [151 3,691,394 Davis [4 1 Sept. 12,1972

[541 FREQUENCY BAND SHIFTER 3,508,075 4/1970 Savage ..328/X 72 Inv to: Robert D. n s Vall 1 an r Calif. pmg ey Primary Examiner-Robert K. Schaefer Assistant Examiner-William J. Smith u Spectral Dynamics Corporation, Attorney-Carl R. Brown et al.

San Diego, Calif.

22 Filed: Aug.25, 1971 ABSTRACT 21 A 1 N ;174, 72 A frequency band shifter for shifting a selected frequency band in a complex waveform, which frequency band is translated with its relative frequen- E CCll. 3071136 Cy phase and amplitude relationships maintained to a I o I a o a u u u i I u I n n a u I I I e n n I a u a u o c u u a n u u ll. a u a I n n u a. and a [58] Field snub smaller frequency band for analysis, which translation is processed by manual or digital control with a master local oscillator control clock that provides protection [56] References Cmd against drift in frequency and phase throughout the UNITED STATES PATENTS y 2,992,326 7/1961 Kahn ..328/l5 X 16 Claims, 7 Drawing Figures I6 28 2 ZERO LF. 30 7 [NPUT ATTENUATOR AMPLIFIER DATA VAR|ABLE AND a Low PASS BANDW'DTH DATA LOW PASS OUTPUT 1o BUFFER HLTER MODULATOR a BANDPASS DEMODULATOR FILTER 34 FILTER EXTERNAL A 83 REF. SIGNAL 1/ 87 EXT. REF

39 5s 85 QUTPUT /3B #OUTPUT MODULATOR so 1 36 mm: a \91 GENETATOR 57 3 84 #80 Ext REE EXT. 5 l l 42 REF. K59 78 6 OUTPUT TV MANUAL PHASE e1 CENTER- 1 48 DE MODULATOR 6 FREQUENCY OCK CARRIER 9| SELECTOR MULTIPLIER GENERATOR ea 50 54 52 I 64 MASTER CLOCK BANDW'DTH FR EOUENCY CLOCK 52 DIVIDRS SWITCHING FREQUENCY BAND SHIFTER BACKGROUND OF THE INVENTION There are known electronic wave analyzers that analyze the amplitudes and phases of frequency components in complex waveforms. Examples of such wave analyzers are octive band analyzers, fraction octive analyzers, constant percentage bandwidth analyzers, distortion analyzers and constant band analyzers. Descriptions of these types of wave analyzers can be found in acoustic measurements by Beranek, Chapter 12, pages 516 through 526. While these analyzers can analyze a single frequency, they are generally used to analyze given bandwidths of an input complex signal that covers a wide frequency band. Thus it is necessary to select and analyze selected bands of frequencies from the input complex waveform or data signal. In many systems it has been found advantageous and necessary to analyze given bandwidths of signals from higher and higher frequencies. Further it is necessary to process the analysis of these bandwidths with computerized systems. However because of the limitations of the computer relative to higher frequencies, the use of computer analysis of higher frequency bandwidths has been limited.

Thus the present invention provides a new and improved frequency band shifter that can select a bandwidth window from a relatively high frequency portion of an input complex signal and translate this bandwidth window down to a much lower frequency, while exactly reproducing the relative frequency, phase and amplitude relationships between the components of the two bandwidths. This permits the analyzing of the data signal at the lower frequency by existing wave analyzers and also permits computer processing of the data information at the lower frequency, that could not be otherwise handled due to the upper frequency limitations of the computer system. The system further allows for more economical use of computer memory by reducing the number of samples that must be taken and stored prior to processing.

SUMMARY OF THE INVENTION In an embodiment of this invention, the complex waveform or input data signal to be analyzed is applied to a balance modulator where it is heterodyned with a high frequency carrier signal. The carrier signal is generated from a fixed reference frequency signal and a second frequency signal that corresponds with the center frequency of the particular bandwidth of the frequencies of the data signal that is to be analyzed. The heterodyned output IF signal is than passed through a phase and amplitude coherent bandpass filter section that employs polyphase modulations to translate the IF frequency down to the audio range, where it is relatively easy to design bandwidth and bandpass filters with the desired flat passband and sharp cut-off 4 characteristics. The signals are filtered and then restored to the original IF frequency.

In the IF bandpass filter, the IF signal is multiplied by the reference oscillator carrier in balanced demodulators in both channels. This essentially translates the IF band of frequencies down to a new band centered at zero Hz, with one of the resulting two sidebands consisting of negative frequencies. The carrier supplied to the lower modulator however, is 90 out of phase so that the resulting lower modulator output is out of phase with the upper channel modulator output. The low pass filters, which are programmed to the desired bandwidth that is normally in the audio range, only passes those IF signal components within the cut-off frequency of the filters that are centered around 0 Hz. The audio range, passband frequencies are then restored to the original IF frequency in a pair of modulators. The second modulator in the lower channel is also driven by the carrier that is 90 out of phase, so that the original IF output frequency is recovered in phase and amplitude with the upper channel. The other side band, however, is degrees out of phase. Thus these signal components cancel each other in the summing circuit, while the desired frequency, phase and amplitude signal components add. The audio range filter characteristics thus are translated to the IF frequency spectrum.

The IF output frequency spectrum is then demodulated with a high frequency carrier signal corresponding to the reference oscillator carrier employed in the IF bandpass filter plus a programmed low frequency that is the center frequency for the translated low frequency data window. A low pass filter removes the higher frequencies leaving the data signal that has been translated to the lower frequency. Thus the frequency, phase and amplitude relationships between components in the input data signal window are translated to the lower frequency. A programmed command can set the bandwidth at the lower frequency to which the selected band frequencies of the input data signal are translated, and also selectively set the center frequency of the lower frequency band.

In this system, a master oscillator or clock provides the frequency signals for the carrier signals and programmed reference signals through voltage controlled oscillators and phase lock loop circuits that hold the entire system to frequency and phase coherence. Thus thesystem selects and separates a band of frequencies from a data signal that may have a relatively high frequency and translates the band of frequencies to a frequency band at a much lower frequency, while maintaining frequency, phase and amplitude relationships between the components of the translated frequency band.

This system also permits the slaving of one frequency band shifter with a second or a plurality of frequency band shifters in an arrangement wherein the particular center frequency setting of the data input signals are set at the same frequency in both frequency band shifters and with the bandwidth being translated and the lower center frequency to which the bandwidth is translated, also being set the same in both frequency band shifters. Thus this system provides identical frequency band shifting of two different complex signals while maintaining the phase and amplitude of both signals in the reproduced new output frequency shifted signals.

It is therefore an object of this invention to provide a new and improved system for selecting a band of frequencies window from a complex input signal and translating the band to a selective lower frequency range.

It is another object of this invention to provide a new and improved system for frequency band shifting selected bandwidths of frequencies from input data signals to lower frequency ranges to permit computer processing of higher frequency data signals and to permit such computer processing in a manner that reduces the computer memory requirements.

It is another object of this invention to provide a new and improved low frequency translator that separates a selected band of frequencies from a data signal and translates the band of frequencies down to a lower frequency band, while maintaining frequency, phase and amplitude relationships of the selected band of frequencies in the lower frequency band.

These and other objects of this invention will become more-apparent upon a reading of the following detailed description and an examination of the drawings wherein like reference numerals designate like parts throughout and in which:

FIG. 1 is a block diagram of a frequency band shifter embodying the present invention.

FIG. 2 is a block diagram illustrating in more detail the master clock, clock frequency dividers, bandwidth switching and demodulator carrier generator of the block diagram illustrated in FIG. 1.

FIG. 3 is a more detailed block diagram of the phase lock multiplier of FIG. 1.

FIG. 4 is a more detailed block diagram of the modulator carrier generator of FIG. 1.

FIG. 5 is a more detailed block diagram of the zero IF variable bandwidth and bandpass filter of FIG. 1.

FIG. 6 is a schematic diagram illustrating the translating of a selected data window to a lower frequency.

FIG. 7 is a block diagram of a slaved connection of frequency band shifters.

Referring now to F IGS.'l and 6, a complex electrical signal or data signal to be analyzed is fed to the input 10 of the attenuator and buffer 12. This complex signal may be provided from any suitable source, such as from a vibration transducer fastened to a vibrating body, or from a microphone exposed to a source of sound, or from a transmitted signal or from any other suitable source that may have a wide range of frequencies of interest, for example, from 10 to 1.5 MHz. It is one of the objects of this invention to select a given bandwidth window from the data signal and translate it down to a lower frequency, such as illustrated in FIG. 6. The translated data window is reproduced at the lower frequency with the relative frequency, phase and amplitude relationship between the components of the input data signal remaining the same.

The input data signal is routed through the attenuator and buffer 12, and through output line 14 with an amplitude that is within the amplitude range of the system. The signal is then passed through the amplifier and low pass filter that removes all frequencies above the upper range of the system. The data signal is then fed to the data modulator where it is mixed with a carrier signal that comprises, for example, a 100 K hertz f frequency, which f corresponds to the center frequency of the data window of the input data signal that is to be translated.

A master clock oscillator 50, FIGS. 1 and 2, provides the output frequency signal for the entire system and on which the frequency outputs of the other voltage control oscillators are phase locked. The master oscillator 50 supplies an output signal, that for purposes of this description, is 300 KHz, through line 52 to a plurality of clock frequency dividers 54. The respective frequency divider circuits 100, 102 and 104 divide the 300 to 100 KHz, which is fed through line 116 to the bandwidth switching circuits 64 and through line 48 to the phase lock multiplier 46 and line 56 to the zero IF variable bandwidth and bandpass filter 24 through line 58 to the loop modulator circuit 130. Dividers 106, I08 and 110 respectively provide frequency signals of 60 Hz, 30 Hz, and 6 Hz through lines 114, 112 and 118 to the bandwidth switching circuits 64. The bandwidth switching circuits 64 are controlled by programmed input signals, such as BCD input information or other suitable input programmed information that provides proper signal levels to switch particular ones of the input frequencies, 6 Hz, 30 Hz or 300 Hz, to line 68. Line represents a plurality of lines 66 that feed digital programmed signals to lines 72 for'selectively closing bandwidth switches in the bandwidth switching circuits that connect a particular output of the voltage controlled oscillators 134, 136, 138 and 140 through lines 78 to output line 82. For this description, the VCO 134 provides an output frequency signal centered around 100,300 Hz, VCO 136 provides an output 100,060 Hz, VCO 138 provides an output of 100,030 Hz with VCO 140 providing an output of 100,006 Hz. The respective VCOs are energized by a signal through the bandwidth switching circuit, line 68, frequency phase detector 120, error integrator 122, and through line 132 to the respective VCO.

Thus the bandwidth switching circuits 64 and 80, select a particular center frequency that is divided down from the 300 KHz master clock input signal and they also select the corresponding local oscillator VCO 134, 136, 138 and 140. For purposes of this explanation, it is assumed that the center frequency chosen is 6 Hz and therefore the output of the VCO 140 of 100,006 Hz is selected. This 100,006 Hz signal is applied through line 84 to the loop demodulator 130 with the carrier frequency of KHz from line 58 also applied to the loop demodulator 130. The modulators output is the upper and lower sidebands, with the carrier of 100,006 I-Iz suppressed. The low pass filter 128 removes the uppersideband and feeds the lower sideband of 6 Hz to the limiter amplifier 124 and through line 126 to the frequency phase detector circuit 120.

The frequency phase detector compares the frequency received from line 126 to the actual input frequency from line 68. If the VCO frequency is not 6 Hz greater than the clock frequency of 100 KHz, then the filter signal in line 126 is not 6 Hz and the detector produces an error signal. The error signal is integrated by the error integrator 122 and used to correct the output frequency of the VCO 140. It will be recognized that any frequency error in the VCO 140 output, with respect to the 100 KHz clock, is due solely to the 6 Hz loop input, which is derived from the master clock input signal. Since this would be only 0.001 percent of the error in the clock itself, there is effectively no error in the data demodulator carrier frequency with respect to the 100 KHz clock frequency. The output of line 82 is fed to the data demodulator 28 for purposes that will be described in more detail hereinafter.

To select the modulator carrier frequency to be fed to the data modulator 20 to establish the center of frequency of the data frequency band to be translated,

a signal is fed through line 48 from the clock frequency dividers 54 to the phase lock modulator circuit 46. In this example, the signal is divided down to 50 Hz.

The phase lock loop multiplier 46 functions as a digitally controlled oscillator to provide an output frequency that may be controlled by a computer programmed input, or by a manual BCD encoder, or by any other suitable means. The input signal of 50 Hz is fed through line 48, see FIG. 3, to a frequency and phase detector 142. In this description of the phase loop multiplier 46 and the manual center of frequency selector 42, the m frequency is the'center frequency that is set manually in the BCD encoded 42 and f is the center frequency of the signal supplied out line 40, with the'two signals being numerically equal. The multiplier is principally a phase lock loop that incorporates a selectable divider. The selectable divider consists of the BCD encoder 42 on which the center frequency m is set manually. The BCD register 146 registers the count of the VCO 146 output pulses that are fed through line 148, automatic switching circuits 160 and 164 to the BCD register 166. The BCD registers feed the register count through lines 168 to the comparator gates 170 where the contents of the BCD register are compared with the encoder information fed through lines 44. When the contents of the BCD register 166 and the BCD encoder 42 coincide, the comparator 170 produces an output pulse that resets the BCD register through lines 172 and 176. Thus the frequency of this reset pulse is the VCO frequency divided by m which should be the 50 Hz signal.

This reset pulse is also applied through line 174 to the frequency and phase detector 142. If the VCO 146 frequency is not m times the 50 Hz input frequency, then the comparator output is not 50 Hz and the detector 142 produces an error signal. This error signal is integrated and fed to the VCO 146 to correct the VCO 146 frequency output. Thus the VCO frequency output to lines 148 and 150 is always in times the 50 Hz signal.

To limit the frequency range of the VCO 146, loop dividers 158, output dividers 154 and automatic switching circuits 156 and 160 function in combination with a return signal 162 from the comparator gate 170 to provide selective divisions of the VCO frequency output so that the VCO 146 only has to operate on a single decade for all of the three highest decades of the center frequency. The output dividers 154, switch in synchronism with the loop dividers 158, and restore the VCO 146 frequency to the proper decade while they simultaneously divide out the original 50 Hz loop input frequency. Thus the multiplier output frequency f is equal to the setting m on the manual BCD encoder 42.

The selected center frequency f which may be, for example, 9,000 Hz, is fed through line 40 to the modulator carrier generator circuit 36, see FIG. 4. The function of the modular carrier generator circuit 36 is to convert the center frequency f into the reference frequency f,, which is the f frequency plus the 100 KHz carrier frequency. This circuit is essentially a phase lock loop translator. The frequency and phase detector 178 feeds a output signal through line 192 to an error integrator circuit 180 that feeds an error signal to a VCO 182. A signal received by the error integrator 180 is summed with the output of the digital clamp circuit 184 to which is fed the 100 KHZ clock input signal through line 60. Line 60 also supplies the IOO'KI-Iz clock signal to the demodulator 186. The output of the VCO oscillator 182 is supplied through line 38 to the data demodulator circuit 120 and is also returned through feedback loop 198 to-the demodulator 186. The balance demodulator 186 and the low pass filter 188 are the elements within the phase lock loop that causes it to translate. The demodulator 186 output is the upper and lower sidebands of the f frequency and 200 KHz plus the f frequency. The low pass filter 188 removes the upper sideband and feeds the f frequency through line 204, limitor amplifier 190 and line 206 to the frequency and phase detector 178. If the VCO 182 frequency f, is correct to 100 KHZ plus f then the output of the low pass filter 188 is the f frequency, which is the loop input frequency. If the low pass filter 188 output is not the f frequency, then the phase detector 178 makes the comparison and feeds an error signal that is integrated by the error integrator 180 to raise or lower the frequency output of the VCO 182. While the translation loop will not correct for VCO frequencies below the 100 KHZ clock frequency, the digital clamp circuit clamps to above 100 KHZ and provides a phase detector error signal output to the summing junction 196 of error integrator 180, if the VCO 182 output frequency falls below the clock signal frequency of 100 KHz.

The reference frequency f, of 100 KHz plus the f frequency is fed through line 38 and closed switch 41 to the data modulator 20.

In the data modulator 20, the input data signal is mixed with f, carrier frequency or the 100 KHz f carrier. The carrier is suppressed leaving sidebands 100 KHZ 2 f and 100 KHZ. Each sideband contains all of the amplitude and phase information of the original data signal. These sidebands are fed through line 22 to the zero IF demodulators 214 and 216. The 100 KHz carrier signals from line 56 that are applied to the zero IF demodulators and modulators are displaced in line 210 from line 212 by the 90 phase shifter 208. Thus the input complex signal is applied to both the CO zero IF demodulator 214 and the QUAD zero IF demodulator 216. The KHz carrier signals applied to the balanced zero IF demodulators 214 and 216 are displaced in the demodulation process, with the remaining output of both demodulator outputs to lines 228 and 230 containing signals f 1 f, and f f which for this example f represents all the frequencies greater than f that are within the filter bandpass and f represents all the frequencies lower than f that are within the filter bandpass. Also included is a DC component that is proportional to thepriginal data components at f Because the 100 KHz CO and QUAD carriers are displaced by 90, the functions of the higher frequency CO signal components (f if phase-lead the corresponding QUAD signal components. Conversely, the functions of the lower frequency CO signal components (fig-f phase-lag the corresponding QUAD signal components. Hence, although f if may be equal to f f; in frequency, they are not in phase and therefore some frequency information has been transformed into phase informatron.

The low pass filters 218 and 220 may, for example, be 6-pole Tchebycheff filters or any suitable and selectable bandwidth, bandpass filters that are controllable by the input bandwidth signals in line 74. Thus these filters are programmable to a given bandwidth, bandpass spectrum around The CO frequencies. of interest (f f at zero degrees) represents only those frequencies that lie above the center frequency, and the QUAD frequencies of interest (f f at zero degrees) represent those that lie below. Therefore, the cut-off frequency of each variable low-pass filter is only one-half the desired total bandpass.- The resistive elements of each filter pole are connected through relays, and the relays operate as a function of the bandwidth switching logic applied through line 74 to the relay drivers. Thus, the cut-ofi frequency of the filters is automatically selected to match the analysis range of bandwidth desired. The signal through line 74 can also be provided from an external reference source 73 through switch 97. This external reference signal can provide any desired analysis range of bandwidths desired irrespective of the translation.

After filtering, which leaves only the component of data within the filter pass band, the CO and QUAD zero IF signals are modulated with the 100 KHZ CO and QUAD reference signals in zero IF modulators 222 and 226 to restore the 100 KHz IF and attendant sidebands. When the CO and QUAD 100 KHZ IF signals are linearly added in linear adder 224, the lower CO sidebands 100 KHz (f -f and the upper QUAD sidebands, 100 KHz (f, f,.,,) are cancelled. The remaining components, 100 KHz, 100 KHz (f f and 100 KHz (f f retain their original frequency spacing; and for example, iff isf 5 Hz, then 100 KHz (f -f,) is 100,005 Hz. A decrease in the input frequency causes an increase in the output frequency because the lower sideband is taken from the data IF modulator. The demodulator 28 reverses this effect as it translates the frequency downward. The relative amplitude and phase of the original signals are also preserved, and the output components of the dynamic bandpass filter are amplitude and phase coherent with the input data that lies within the pass band.

The zero IF variable bandwidth and bandpass filter 24 transmits only the 100 KHz sideband through line 26 to the data demodulator 28. In the case of a complex data signal, other sideband components are also transmitted according to the selected bandwidth of the filter 24. In the data demodulator 28, the filtered signal is combined with a new carrier whose frequency is that supplied through line 82 and is 100 KHZ +f and where f is the new center frequency of the band to which the data is being translated. The carrier is suppressed, leaving the lower sideband, f' which still contains the original amplitude and phase information. The low pass output filter 32 removes the upper sideband and the translated data is supplied through line 34.

Thus it may be understood that the frequency componentf supplied through line 38 to the data modulator sets the center frequency of the portion of the input data signal that is to be translated, with the control signal through line 74 to the variable bandwidth, bandpass filters 220 and 218, setting the bandwidth spectrum around the fm frequency that is being translated, and the f portion of the signal in line 82 to the data modulator 28 setting the center frequency of the translated data window output. All of the signals aforesaid, are programmed by either the manual center frequency selector 42 or the input computer programmed information in lines 66. The manual center frequency selector can set the center frequency for any frequency within the general range of the input signal in line 10. The bandwidth switching circuit in response to the input program information may set up bandwidth and translated center frequencies in, as an example in this embodiment, 6 Hz, 30 hz, 60 hz and 300 hz increments.

In a modified embodiment of this invention, a pair of frequency band shifters A and B, see FIG. 7, can be employed in a slave arrangement to provide frequency band shifting of input data signals to provide output signals that may be processed at a lower and more usable frequency spectrum, where the amplitude and phase of the signals retain the same amplitude and phase of the input signals. This arrangement may be used in automatic and cross correlation work for processing two signals in data analyzers where the information is fed into a phase and amplitude analyzer that uses a computer programmed sample data system. In this embodiment, the frequency band shifter A corresponds to the frequency band shifter illustrated in FIG. 1 and the frequency band shifter B is a frequency band shifter that is identical to the frequency band shifter of FIG. 1. In the connection of the two units, line 39 is connected to a line 37 in the frequency band shifter B, in which switch 41 in frequency band shifter B is closed to line 37. Line 57 of frequency shifter B is connected to line 61 of frequency band shifter A and switch 59 of frequency band shifter B is switched to line 57. Line is connected to line 83 of the frequency band shifter B and in frequency band shifter B, switch 87 is moved into contact with line 83. Also line 91 can be connected to line 73 in frequency band shifter B if desired. Thus the programmed frequency control information of frequency band shifter A is directly connected to control in frequency band shifter B the data modulator 20, the zero. IF variable filter 24, and data modulator 38, to the same center frequency of the input signal to be analyzed, the same bandwidth of the data signal to be analyzed, and the translated lower signal output to the same lower frequency.

I-Iaving described my invention, I now claim:

1. In a frequency band shifter for shifting a selected bandwidth of frequencies of a complex signal,

means for providing a reference signal having a given frequency,

means for providing a second signal having a frequency corresponding to selected center frequency of a particular bandwidth of frequencies in the complex signal,

means for summing the reference signal with said second signal and producing a carrier signal,

data modulator means for modulating said carrier signal with the complex signal producing translated signals,

means for polyphase modulating the translated signals with the reference signal producing an output signal band having the center frequency of the reference signal and the amplitude and phase of the frequency band of interest in the complex signal,

means for providing a demodulating carrier signal having a frequency slightly greater than said reference signal, and data demodulator and filter means for modulatlng said demodulating carrier signal with said output signal band and filtering the demodulated output producing a bandwidth of frequencies having a center frequency corresponding to the frequency difference between said reference signal and said demodulating carrier signal. 2. In a frequency band shifter as claimed in claim 1, including,

a master oscillator for providing a master output frequency signal, and means for locking the phase of said reference signal, said second signal and said programmed low frequency signal to said master frequency signal. 3. In a frequency band shifter as claimed in claim 1 in which,

said polyphase modulating means includes demodulator means for translating said translated signals down to audio range, phase and amplitude coherent bandpass filter means for filtering said translated signals, and modulator means for translating said filter signals to the frequency of the reference signal. 4. In a frequency band shifter as claimed in claim 3 in which,

said bandpass filter means comprises zero IF variable bandwidth and bandpass filters, and means for providing a signal that selectively sets the frequency range of the bandwidth of said bandpass filters. 5. In a frequency band shifter as claimed in claim 4 including,

means for providing a programmed signal determinative of the selective bandwidth of the complex signal translated, and said zero IF bandpass filters being responsive to said signal for setting the bandwidth of said filters. 6. In a frequency band shifter as claimed in claim 1 in which,

said polyphase modulating means having first and second circuit channels, each of said circuit channels having phase and amplitude coherent bandpass filter sections, and means for supplying a bandpass controlling signal to said bandpass filter sections for controlling the bandwidth of said bandpass filter sectrons. 7. In a frequency band shifter as claimed in claim 1 in which,

said polyphase modulating means comprising first and second circuit channels, each of said channels having a demodulator for receiving the translated signals, connected in series with a variable bandwidth and bandpass low 4 pass filter connected in series with a modulator, means for supplying said reference frequency to each of the demodulators and modulators in the first channel and supplying the reference frequency with a 90 phase shift to the demodulators and modulators in the second channel, and summing means for summing the output signals from the modulators in each of the channels.

8. In a frequency band shifter as claimed in claim 7 including,

means for providing a programmed signal to each of said variable bandwidth and bandpass filters, and said variable bandwidth and bandpass filters having their pass-band set by said programmed input signal. 9. In a frequency band shifter as claimed in claim 1 including,

encoder means for providing an output signal corresponding to a selected frequency signal, phase lock multiplier means responsive to said master output frequency signal and said signal from said encoder for providing said second signal that is phase locked to said master output frequency signal, and said summing means for summing the reference signal to said second signal having means for phase locking said carrier signal to said master output frequency signal. 10. In a frequency band shifter as claimed in claim 9 including,

bandwidth switching means responsive to said master output frequency signal and input control signals for providing said demodulator carrier signal which demodulating carrier signals are phase locked to said master output frequency signal. 11. The method of translating a selected bandwidth of frequencies of a complex signal to a lower frequency band while preserving phase and amplitude coherence comprising the steps of,

modulating the complex signal with a signal comprising a reference frequency plus a second frequency corresponding to the center frequency of the selected bandwidth of the complex signal to be translated,

passing the modulated output through a phase and amplitude coherent bandpass filter section that employs polyphase modulation to translate the modulated output down to the audio range,

and raising the filtered output to the frequency of the lower frequency band to which the selected band width of frequencies of the complex signal is being translated.

12. The method of claim 11 including the step of,

selectively varying the bandwidth of the bandpass filter section to selectively vary the bandwidth of frequencies of the complex signal that are translated.

13. In the method of claim 12 including the step of,

selectively setting the center frequency of the lower frequency band to which the selected bandwidth of frequencies of the complex signal are translated to a frequency that in conjunction with the selected bandwidth of the bandpass filter section, maintains the lower frequency band above zero frequency.

14. In the method of claim 13 including the step of,

phase locking the reference signal and the second frequency and the center frequency signal of the lower frequency translated band to the phase of a master oscillator output.

15. In the method defined in claim 14 including the step of,

modulating the output of the bandpass filter section with said reference frequency,

3 ,69 l ,3 94 0.1. 71. demodulating said modulated output with a signal 16. In the method clairned in claim 14 including the comprising said reference frequency and the step f Selected center frequency of the lower frequency controlling the center frequency the lower frequency "anslated band t l t d b d b t r r mm d and filtering the demodulated output to the lower tans a e an y comp erp 0g am c an frequency translated band. 

1. In a frequency band shifter for shifting a selected bandwidth of frequencies of a complex signal, means for providing a reference signal having a given frequency, means for providing a second signal having a frequency corresponding to selected center frequency of a particular bandwidth of frequencies in the complex signal, means for summing the reference signal with said second signal and producing a carrier signal, data modulator means for modulating said carrier signal with the complex signal producing translated signals, means for polyphase modulating the translated signals with the reference signal producing an output signal band having the center frequency of the reference signal and the amplitude and phase of the frequency band of interest in the complex signal, means for providing a demodulating carrier signal having a frequency slightly greater than said reference signal, and data demodulator and filter means for modulat1ng said demodulating carrier signal with said output signal band and filtering the demodulated output producing a bandwidth of frequencies having a center frequency corresponding to the frequency difference between said reference signal and said demodulating carrier signal.
 2. In a frequency band shifter as claimed in claim 1, including, a master oscillator for providing a master output frequency signal, and means for locking the phase of said reference signal, said second signal and said programmed low frequency signal to said master frequency signal.
 3. In a frequency band shifter as claimed in claim 1 in which, said polyphase modulating means includes demodulator means for translating said translated signals down to audio range, phase and amplitude coherent bandpass filter means for filtering said translated signals, and modulator means for translating said filter signals to the frequency of the reference signal.
 4. In a frequency band shifter as claimed in claim 3 in which, said bandpass filter means comprises zero IF variable bandwidth and bandpass filters, and means for providing a signal that selectively sets the frequency range of the bandwidth of said bandpass filters.
 5. In a frequency band shifter as claimed in claim 4 including, means for providing a programmed signal determinative of the selective bandwidth of the complex signal translated, and said zero IF bandpass filters being responsive to said signal for setting the bandwidth of said filters.
 6. In a frequency band shifter as claimed in claim 1 in which, said polyphase modulating means having first and second circuit channels, each of said circuit channels having phase and amplitude coherent bandpass filter sections, and means for supplying a bandpass controlling signal to said bandpass filter sections for controlling the bandwidth of said bandpass filter sections.
 7. In a frequency band shifter as claimed in claim 1 in which, said polyphase modulating means comprising first and second circuit channels, each of said channels having a demodulator for receiving the translated signals, connected in series with a variable bandwidth and bandpass low pass filter connected in series with a modulator, means for supplying said reference frequency to each of the demodulators and modulators in the first channel and supplying the reference frequency with a 90* phase shift to the demodulators and modulators in the second channel, and summing means for summing the output signals from the modulators in Each of the channels.
 8. In a frequency band shifter as claimed in claim 7 including, means for providing a programmed signal to each of said variable bandwidth and bandpass filters, and said variable bandwidth and bandpass filters having their pass-band set by said programmed input signal.
 9. In a frequency band shifter as claimed in claim 1 including, encoder means for providing an output signal corresponding to a selected frequency signal, phase lock multiplier means responsive to said master output frequency signal and said signal from said encoder for providing said second signal that is phase locked to said master output frequency signal, and said summing means for summing the reference signal to said second signal having means for phase locking said carrier signal to said master output frequency signal.
 10. In a frequency band shifter as claimed in claim 9 including, bandwidth switching means responsive to said master output frequency signal and input control signals for providing said demodulator carrier signal which demodulating carrier signals are phase locked to said master output frequency signal.
 11. The method of translating a selected bandwidth of frequencies of a complex signal to a lower frequency band while preserving phase and amplitude coherence comprising the steps of, modulating the complex signal with a signal comprising a reference frequency plus a second frequency corresponding to the center frequency of the selected bandwidth of the complex signal to be translated, passing the modulated output through a phase and amplitude coherent bandpass filter section that employs polyphase modulation to translate the modulated output down to the audio range, and raising the filtered output to the frequency of the lower frequency band to which the selected band width of frequencies of the complex signal is being translated.
 12. The method of claim 11 including the step of, selectively varying the bandwidth of the bandpass filter section to selectively vary the bandwidth of frequencies of the complex signal that are translated.
 13. In the method of claim 12 including the step of, selectively setting the center frequency of the lower frequency band to which the selected bandwidth of frequencies of the complex signal are translated to a frequency that in conjunction with the selected bandwidth of the bandpass filter section, maintains the lower frequency band above zero frequency.
 14. In the method of claim 13 including the step of, phase locking the reference signal and the second frequency and the center frequency signal of the lower frequency translated band to the phase of a master oscillator output.
 15. In the method defined in claim 14 including the step of, modulating the output of the bandpass filter section with said reference frequency, demodulating said modulated output with a signal comprising said reference frequency and the selected center frequency of the lower frequency translated band, and filtering the demodulated output to the lower frequency translated band.
 16. In the method claimed in claim 14 including the step of, controlling the center frequency the lower frequency translated band by computer program command. 